1. Technical Field
The present invention relates generally to fuel control systems and, more particularly, to a method of controlling the combustion parameters of an internal combustion engine in a flexible fueled vehicle.
2. Discussion
Environmental and energy independence concerns have stimulated the development of alternative transportation fuels, such as alcohol fuels, for use in automobiles. Alcohol fuels include methanol and ethanol. A flexible fueled vehicle capable of operating on gasoline, or alcohol fuel, or any mixture of the two fuels, is therefore in demand. Modifications to the engine are necessary when operating on different fuels because of the different characteristics of each fuel. For example, an engine operating on ethanol or E85 (a blend of 85% ethanol and 15% gasoline) requires approximately 1.4 times the amount of fuel relative to gasoline at stoichiometry due to a lower energy content of the ethanol.
Air/fuel ratio in internal combustion engine design is typically considered to be the ratio of mass flow rate of air to mass flow rate of fuel inducted by an internal combustion engine to achieve conversion of the fuel into completely oxidized products. The chemically correct ratio corresponding to complete oxidation of the products is called stoichiometric. If the air/fuel ratio is less than stoichiometric, an engine is said to be operating rich, i.e., too much fuel is being burned in proportion to the amount of air to achieve perfect combustion. Likewise, if the air/fuel ratio is greater than stoichiometric, an engine is said to be operating lean, i.e., too much air is being burned in proportion to the amount of fuel to achieve perfect combustion. Alcohol fuels have a lower air/fuel ratio than gasoline at stoichiometric, so that the engine must be compensated for in the rich direction as the percentage of alcohol in the fuel increases.
There are several sensors that are not necessarily flexible fuel operation specific but which are used as inputs for flexible fuel compensation control systems. These include, but are not limited to, a coolant temperature sensor, battery temperature sensor, upstream exhaust oxygen sensor, vehicle speed sensor, and fuel level sensor.
When any one of these sensors is in error, its output cannot be used as an input for the fuel compensation control system. For instance, if the coolant sensor errors, there is no way to realize the coolant temperature and no way to detect a boil-off condition or when the internal combustion engine reaches a fully warm condition. If the battery temperature sensor errors, there is no way to sense battery temperature and no way to determine if a boil-off condition is occurring. If the upstream exhaust oxygen sensor errors, there is no feedback data for basing a determination of the fuel composition multiplier for setting fueling parameters in a fuel control system. If the vehicle speed sensor errors, there is no way to determine when the vehicle has come to a stop which may correspond to a fueling event. If a fuel level sending unit errors, there is no way to measure a fuel addition.
Therefore, it would be desirable to provide a method for compensating for erroring sensors in a flexible fuel compensation control system for a flexible fueled vehicle.